Study Finds
Correlation Between Pesticides and Reduced Male Fertility
(Beyond Pesticides, January 19, 2006) A study
published in the January issue of Epidemiology has found inverse associations
between pesticides and male testosterone levels. The study, conducted
by researchers at University of Michigan, Harvard University, and the
Centers for Disease Control and Prevention in Atlanta, has found that
high levels of the urinary metabolites of chlorpyrifos
(TCPY) and carbaryl
and naphthalene
(1N) correlate directly with low levels of testosterone in male subjects.

The researchers
studied urine samples from 268 male clients of a Massachusetts fertility
clinic between 2000 and 2003. The results of the study found an inverse
correlation between high levels of the urinary metabolites and low levels
of testosterone. The researchers feel that the study is environmentally
relevant since the levels of TCPY and 1N found in the subjects is consistent
with the results of national studies looking at human pesticide exposure.

Environmental exposure
to these chemicals is not a new discovery. According to the researchers,
“The Second National Report on Human
Exposure to Environmental Chemicals (carried out within NHANES 1999-2000)
found that more than 90% of males in the U.S. population had urine samples
with detectable levels of TCPY…The Report also found that over
75% of U.S. males have detectable levels of 1N.” Although residential
use of chlorpyrifos, a broad-spectrum organophosphate, was highly restricted
in 2000, high rates of TCPY are still being found in urine. Exposure
is most likely continuing due to the environmental persistence of the
pesticide. Although chlorpyrifos is commonly referred to as “nonpersistent”,
it can persist for an extended period of time if in the right conditions.
Trace amounts of chlorpryifos continue to be found in many different
foods, also providing a common exposure route.

The researchers
believe that the correlation between the pesticides and reduced male
fertility may be due to the enzyme disruption associate with the chemicals.
Chlorpyrifos is a known cholinesterase inhibitor, which the researchers
believe may affect the release of luteinizing hormone (LH), the hormone
that triggers testosterone secretion from the Leydig cells.